For columns with different cross section types, the confinement of the longitudinal bar offered by the stirrups was different, which influences the spring stiffness p of the simplified buckling model.
The spring stiffness coefficient p of circular cross sections is larger than that of rectangular cross sections, as indicated in Tables 1 and 2.
Thus, the buckling length of the longitudinal bar in rectangular columns is larger than that of the circular columns, as shown in Table 6.
Consequently, the hysteresis loops of the circular units are considerably broader, and the columns with circular cross sections show better displacement ductility and energy dissipation than those with rectangular cross sections with the same stirrup diameter and spacing, as indicated in Table 6.
Thus, the cross section type has an obvious effect on the spring stiffness coefficient p and therefore on the seismic performance of the RC columns